Cutting and profiling techniques for stainless steels

Introduction

Stainless steel can be cut and profiled in the same way and using the same type of equipment as for most other steels. Some differences in technique apply and these are explained below. The information in this article is specifically directed towards austenitic stainless steels, the most frequently used family of stainless steels.

Austenitic stainless steels exhibit strong work hardening characteristics which affect many of the forming techniques. Machinery capability levels need to be increased (or existing capability levels down-rated) compared with carbon steels. A higher rigidity of tools and machinery is necessary for working stainless steel.

All fabrication processes should be carried out in a clean, and if possible, a dedicated environment.

The first operation undertaken in the fabrication workshop is that of cutting bulk materials into appropriate work pieces. This is readily achieved using existing machinery although in some cases the use of a specialist subcontract facility will be to advantage.

Sawing

A power hacksaw operated at nominally 80 strokes per minute with some 0.08 mm feed per stroke will give satisfactory results. At all times ensure a positive feed and avoid rubbing, which will induce glazing and work hardening of the metal. High-speed band saws work well on stainless steels with a speed of some 18 metres per minute

Shearing

Conventional press/guillotine equipment is used for shearing stainless steels, but should normally be down-rated by 40% compared with their carbon steel rating. Blades and cutters should be well adjusted with edges maintained sharp, thus avoiding the dragging of metal over the blade which would lead to work hardening. The same considerations should apply in working the nibbler to cut out shapes in sheet metal.

Plasma cutting

This process is usually employed to produce shapes from plate material. A clean cut edge and minimum distortion are provided, but it should be noted that a slight taper is provided to the cut edge and due allowance should be made in the design and finishing of the component.

Blanking, punching and piercing

Each of these processes is mechanically the same in that each is an extension of the shearing operation previously referred to. The machinery used, punches and dies, must have adequate strength and rigidity to accommodate the added power used.

In blanking operations die clearances have to be controlled and a figure of 5% metal thickness per side is quoted for popular gauge thickness. Excessive clearances lead to the metal being dragged with resulting burrs to the blank.

In piercing and punching, hole sizes should not be less than 1.5 times the metal thickness. To avoid excessive distortion, the distance between holes should not be less than one half of the hole diameter.